1. Field of Invention
The invention relates to a hydraulic control device for a work machine.
2. Description of Related Art
Generally, some work machines have a plurality of hydraulic actuators, a hydraulic pump to feed pressurized oil to the hydraulic actuators, control valves operating so as to control feed of the pressurized oil to the respective hydraulic pumps, and a control unit to output control commands to an actuator of the control valves by inputting operation signals from operating tools. For the hydraulic control system, there is a closed center system in which oil is not bled when the control valve is at the neutral position. Conventionally in such a closed center system, the degree of openness (spool positions) of the respective control valves is constructed so that the degree is controlled in response to the degree of operation of an operation tool corresponding thereto regardless of the operating status of the other operation tools.
However, where a plurality of operation tools are operated in combination, the flow requested by the respective hydraulic actuators required for operating the corresponding operation tools can exceed the flow which the hydraulic pump can feed. In such cases, the amount of pressurized oil supplied into the hydraulic actuators, passing through the respective control valves, becomes less than the requested volume. However, because the degree of openness of the respective control valves is controlled in response to the operating degree of the operation tools corresponding thereto, as described above, the operating degree may be increased more than the feeding volume of the hydraulic pump. In such a case, the hydraulic actuators may become vacuous, resulting in inadequate movement. For example, smooth actuation is hindered when a front attachment attached to a work machine is interlocked therewith and actuated. Another problem occurs in that the operation efficiency may be worsened.
In various exemplary embodiments of the hydraulic control device for a work machine according to the invention, the hydraulic control device for a work machine includes a plurality of hydraulic actuators, a hydraulic pump for feeding pressurized oil to the hydraulic actuators, control valves for controlling the feeding of pressurized oil to the respective hydraulic actuators, and a valve operating means for operating the respective control valves. The hydraulic control device also includes a control unit which inputs signals coming from an operation status detector for detecting the operation status of the operating tools for the respective hydraulic actuators and outputs control commands to the valve operator corresponding thereto on the basis of the corresponding input signals wherein the corresponding control unit calculates the amount of flow for sharing the output flow of the hydraulic pump to the respective hydraulic actuators on the basis of input signals from the operation status detector and outputs control commands to the valve operator in order to feed the corresponding shared flow to the respective hydraulic actuators.
As such, the control valves operate so as to supply the shared flow to the respective hydraulic actuators, wherein when operating a plurality of hydraulic actuators in combination, the output volume of the hydraulic pump can be adequately shared to the respective hydraulic actuators, and, at the same time, it is possible to prevent the degree of openness of the control valve from becoming greater than the supply volume from the hydraulic pump, whereby its composite operation efficiency can be improved.
Thus, it is possible to calculate the output flow of the hydraulic pump on the basis of the maximum torque, number of revolutions, and discharge pressure of the pump.
Also, in a case where the sum of the requested flows of the respective hydraulic actuators required on the basis of the operating status of an operating tool is smaller than the output flow of the hydraulic pump, it is possible to prevent the shared flow from becoming greater than the requested flow by setting the requested flows of the respective hydraulic actuators to the shared flow.